Kd. Clark et al., ISOLATION AND IDENTIFICATION OF A PLASMATOCYTE-SPREADING PEPTIDE FROMTHE HEMOLYMPH OF THE LEPIDOPTERAN INSECT PSEUDOPLUSIA-INCLUDENS, The Journal of biological chemistry, 272(37), 1997, pp. 23440-23447
Insect blood cells (hemocytes) play an essential role in defense again
st parasites and other pathogenic organisms that infect insects. A key
class of hemocytes involved in insect cellular immunity is plasmatocy
tes. Here we describe the isolation and identification of a peptide fr
om the moth Pseudoplusia includens that mediates the spreading of plas
matocytes to foreign surfaces. This peptide, designated plasmatocyte-s
preading peptide (PSP1), contains 23 amino acid residues in the follow
ing sequence: H-ENFNGGCLAGYMRTADGRCKPTF-OH. In vitro assays using the
synthetic peptide at concentrations greater than or equal to 2 nM indu
ced plasmatocytes from P. includens to spread an the surface of cultur
e dishes. Injection of this peptide into P. includens larvae caused a
transient depletion of plasmatocytes from circulation, Labeling studie
s indicated that this peptide induced 75% of plasmatocytes that were d
ouble-labeled by the monoclonal antibodies 49G3A3 and 43E9A8 to spread
, whereas plasma induced significantly more plasmatocytes to spread, T
his suggests that only a certain subpopulation of plasmatocytes respon
ds to the peptide and that other peptidyl factors mediate plasmatocyte
adhesion responses.